are people expected to work extra hours for free in the US?

Depends on the kind of work you're doing. Under American labor law, workers in retail, manufacturing, or the trades can't be asked to work more than eight hours a day or forty hours a week without being paid their hourly wages plus a substantial overtime bonus. However, there's a loophole. American workers in clerical, administrative, and professional positions -- those on the administrative side of historical labor disputes, in other words -- are usually paid a fixed yearly income (salaried, or "exempt") and are not eligible for overtime pay.

This has both advantages and disadvantages. The advantage is that the hours are usually more flexible and there's less administrative overhead; the disadvantage is that people that want to signal loyalty or overachievement are incentivized to work crazy hours without extra pay, a practice that employers often encourage, or even -- though usually only in the short term -- de-facto require. Most studies I've read find that actual productivity doesn't go up much with the extra hours in the long run, especially for knowledge workers, but it occasionally does make business sense to do a hard push right before a deadline -- and, of course, managers aren't always rational about these things.

Generally speaking, within IT, operations people are paid hourly and developers are paid on salary. This can make salary figures a little misleading, depending on corporate culture; more than once I've had friends in ops whose nominal wages were considerably lower than mine, but whose actual pay, after overtime, was well higher for the same hours. (I'm in dev.) I try not to make a habit of working those long hours, though.

People are widely expected to work extra hours for free in IT.

This subthread started with CronoDAS pointing out that it's hard to change the amount of money you earn by changing the amount of hours you work, and CoffeeStain pointing out that even if you can't do so in the short run you still can in the long run, because the more you work the more likely you are to be promoted. So, if we talk about the people who can just decide to work more hours this month to earn more money this month, we've come full circle here.